U.S. patent number 6,969,022 [Application Number 10/683,704] was granted by the patent office on 2005-11-29 for seat belt retractor.
This patent grant is currently assigned to Key Safety Systems, Inc.. Invention is credited to Matthew Barber, John Bell, Brian Jack, Martyn Palliser.
United States Patent |
6,969,022 |
Bell , et al. |
November 29, 2005 |
Seat belt retractor
Abstract
A seat belt retractor has a rotatable spool for retraction or
payout of seat belt webbing wound thereon, depending upon the
rotation direction of the spool. A locking wheel is attached to one
end of the spool. The spool to is locked to the locking wheel when
a crash is sensed. A force limiter allows further payout of the
seat belt webbing after the spool has locked to the locking wheel,
under the influence of a vehicle occupant's forward momentum. The
force limiter includes a torsion bar attached at one end to the
locking wheel and at the other end to the spool, and a secondary
force limiter mechanism releasably coupled in the force path
between the spool and the locking wheel, and a mechanism for
de-coupling the secondary mechanism after a predetermined number of
turns of the torsion bar. The locking mechanism has a locking
element that is resiliently biased to a position wherein it locks
the spool to the locking wheel and is held out of locking
engagement by the secondary force limiting mechanism. The retractor
is converted into a standard locking retractor after load limiting
ensuring that the vehicle occupant is securely restrained against
secondary impacts.
Inventors: |
Bell; John (Carlisle,
GB), Jack; Brian (Eastriggs, GB), Palliser;
Martyn (Carlisle, GB), Barber; Matthew (Carlisle,
GB) |
Assignee: |
Key Safety Systems, Inc.
(Sterling Heights, MI)
|
Family
ID: |
34520561 |
Appl.
No.: |
10/683,704 |
Filed: |
October 14, 2003 |
Current U.S.
Class: |
242/379.1;
280/805 |
Current CPC
Class: |
B60R
22/3413 (20130101); B60R 2022/286 (20130101); B60R
2022/287 (20130101) |
Current International
Class: |
B65H 075/48 () |
Field of
Search: |
;242/379.1 ;280/805
;297/472,478 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Nguyen; John Q.
Attorney, Agent or Firm: Drayer; Lonnie R.
Claims
What is claimed is:
1. A seat belt retractor comprising: a rotatable spool having a
spool body; a primary force limiting mechanism comprising a torsion
bar attached at one end to a locking wheel and at the other end to
the spool; and a secondary force limiting mechanism releasably
coupled in a force path between the spool and the locking wheel and
a means for de-coupling the secondary force limiting mechanism
after a predetermined amount of twisting of the torsion bar due to
a load applied by a vehicle occupant secured by a seat belt webbing
that is at least partially wound upon the spool, and wherein a
locking means comprises a locking element that is resiliently
biased to a position wherein it locks the spool to the locking
wheel and is held out of locking engagement by the secondary force
limiting mechanism, the locking wheel has a recess therein along
which the locking element slides and an abutment at an end of the
recess against which the locking element rests.
2. A seat belt retractor according to claim 1 wherein the secondary
force limiting mechanism comprises a wire releasably connected
between the spool and the locking wheel.
3. A seat belt retractor according to claim 2 wherein the wire is
releasably connected to the spool.
4. A seat belt retractor according to claim 2 wherein the wire is
housed in a hole in the spool body from which it is pulled during
load limiting.
5. A seat belt retractor according to claim 3 wherein the wire is
housed in a hole in the spool body from which it is pulled during
load limiting.
6. A seat belt retractor according to claim 2 wherein the wire is
drawn onto the locking wheel during load limiting.
7. A seat belt retractor according to claim 3 wherein the wire is
drawn onto the locking wheel during load limiting.
8. A seat belt retractor according to claim 4 wherein the wire is
drawn onto the locking wheel during load limiting.
9. A seat belt retractor according to claim 5 wherein the wire is
drawn onto the locking wheel during load limiting.
10. A seat belt retractor according to claim 2 wherein a thickness,
length and composition of the wire are chosen to suit a vehicle's
crash criteria.
Description
FIELD OF THE INVENTION
The present invention relates to a seat belt retractor and
particularly to a seat belt retractor with a load limiting
function.
BACKGROUND OF THE INVENTION
Traditionally a seat belt retractor has a generally cylindrical
spool on which seat belt webbing is wound. The spool is rotatably
mounted to wind-up or pay out seat belt webbing, depending upon the
direction of rotation. The spool is biased in the wind-up direction
by a clock spring so that the seat belt maintains a relatively low
level force on a vehicle occupant tending to pull him back into the
vehicle seat in a comfortable manner, but allowing him to move
forward to adjust a car radio and so forth. An acceleration sensor
detects acceleration or deceleration above a predetermined level,
as an indication of a crash, and locks the retractor against the
further payout of webbing to securely restrain the vehicle occupant
in the vehicle seat.
Modern seat belt systems include a load limiting function that
allows some controlled payout of the belt webbing before locking
fully, so as to more gradually decrease the momentum of the vehicle
occupant. This is often achieved using a torsion bar mounted
coaxially in the spool. The torsion bar twists about its own axis,
after the spool mechanism is locked and typically allows up to two
turns of the spool. In this way the crash forces felt by the
vehicle occupant increase linearly as the crash forces increase,
until the torsion bar begins to be twisted. The torsion bar stops
twisting when the load applied from the vehicle occupant
diminishes. The locking wheel is locked in position by the lockbar,
but the spool can turn only when the torsion bar torsion bar is
twisted allowing the spool to turn.
In an improved load-limiting seat belt retractor described in
co-pending U.S. application Ser. No. 10/241,489, a second stage of
operation is provided by a wire element housed in the spool body.
The wire element works in parallel with the torsion bar to create a
higher level of load limiting for a predetermined time or distance.
Thus when the crash sensor first senses a crash a first stage of
operation involves both the torsion bar twisting and the wire being
either bent or twisted or pulled out of its housing in the spool to
absorb the crash forces. Then the wire is fully bent, twisted or
extended, depending on the mechanism employed. Then the crash
forces are applied solely to the torsion bar and a second stage of
operation involves only the torsion bar. This second stage with its
lower level of load limiting works in conjunction with an airbag to
share the load.
However, a disadvantage arises if a second impact occurs because
the airbag has deployed due to the first impact and is no longer
effective to share the restraining load with the seat belt
retractor. Hence it is desirable for the seat belt retractor to
revert to working as a standard non load-limiting retractor in the
case of a second impact.
The present invention can provide the advantage of improving the
crash force curve further and effectively restraining the vehicle
occupant during a second impact.
SUMMARY OF THE INVENTION
There is provided in accordance with the present invention a seat
belt retractor comprising: a rotatable spool having a spool body; a
primary force limiting mechanism comprising a torsion bar attached
at one end to a locking wheel and at the other end to the spool;
and a secondary force limiting mechanism releasably coupled in a
force path between the spool and the locking wheel and a means for
de-coupling the secondary force limiting mechanism after a
predetermined amount of twisting of the torsion bar due to a load
applied by a vehicle occupant secured by a seat belt webbing that
is at least partially wound upon the spool, and wherein a locking
means comprises a locking element that is resiliently biased to a
position wherein it locks the spool to the locking wheel and is
held out of locking engagement by the secondary force limiting
mechanism, the locking wheel has a recess therein along which the
locking element slides and an abutment at an end of the recess
against which the locking element rests.
Preferably the secondary mechanism comprises a wire releasably
connected between the spool and the locking wheel.
Preferably the wire is releasably connected to the spool,
preferably between the spool and the locking wheel.
The wire may be housed in at least one hole in the spool body and
pulled out or extracted from the hole during load limiting. It may
be drawn onto the locking wheel.
The thickness, length and composition of the wire are chosen to
suit a vehicle's crash criteria.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially cut-away perspective view of the spool and
locking assembly of a seat belt retractor according to the present
invention.
FIG. 2 is a perspective view of a locking wheel assembly for one
end of the seat belt retractor of FIG. 1.
FIG. 3 is an end view of the locking mechanism shown in FIG. 2
during a first stage of operation labeled as stage one in the graph
of FIG. 9 when load limiting is provided by primary and secondary
load limiting mechanisms working together.
FIG. 4 is a partially cut-away view of the spool and locking
assembly of FIG. 1 from the locking wheel end during a first stage
of operation labeled as stage one in the graph of FIG. 9 when load
limiting is provided by primary and secondary load limiting
mechanisms working together.
FIG. 5 is a partially cut-away perspective view of the seat belt
retractor of FIG. 1 during a second stage of operation labeled as
stage two in the graph of FIG. 9 when load limiting is provided
only by the primary load limiting mechanism.
FIG. 6 shows the locking wheel end of the seat belt retractor of
FIG. 5 during a second stage of operation labeled as stage two in
the graph of FIG. 9 when load limiting is provided only by the
primary load limiting mechanism.
FIG. 7 is a partially cut-away perspective view of the seat belt
retractor of FIG. 1 during a third stage of operation labeled as
stage three in the graph of FIG. 9 when a locking mechanism engages
the spool and locking wheel and there is no load limiting.
FIG. 8 shows the locking wheel end of the seat belt retractor of
FIG. 7 during a third stage of operation labeled as stage three in
the graph of FIG. 9 when a locking mechanism engages the spool and
locking wheel and there is no load limiting.
FIG. 9 is a graph of force against time showing various stages of
operation of the seat belt retractor.
FIG. 10 is a perspective view of a prior art seat belt retractor
that can be adapted to employ the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The seat belt retractor of the invention is of the general form
used in a known seat belt retractor as shown in FIG. 10. The
remaining figures show only the spool and locking assembly part of
the seat belt retractor. It will be evident to a skilled person how
this part is integrated into a full seat belt retractor. Such prior
art seat belt retractors, as shown in FIG. 10, comprise a
cylindrical retractor spool 100 mounted for rotation in a frame 108
to wind in and pay out seat belt webbing (not shown). A crash a
sensor, positioned generally at 130, but not specifically
illustrated, activates a locking mechanism to move a lockbar 110 to
engage teeth on a locking ring 103 which is fixed to one end of the
spool 100. Subject to further movement due to load limiting
arrangements the spool 100 is then locked against further rotation.
The other end of the spool is connected to a rewind spring
mechanism 105 that comprises a clock type coiled spring that biases
the spool 100 to a webbing rewind condition.
FIG. 1 is a partially cut-away perspective view of the spool and
locking assembly of a seat belt retractor according to the present
invention. In FIG. 1 a hollow spool 1 is shown partially cut-away
with a locking assembly 2 at one end and a torsion bar 3 arranged
along its axis. The torsion bar 3 is fixed to the spool 1 at the
left end as shown in FIG. 1 by splines 21. The torsion bar is fixed
to the locking assembly 2 at the left end as shown in FIG. 1 by
splines 11 fitting in a correspondingly shaped hole in the locking
assembly 2. Although not shown, seat belt webbing is wound around
the outside of the spool 1 and the spool is supported in a frame
for rotation about its longitudinal axis. A rewind spring for the
spool 1 is mounted to the left end, as shown in FIG. 1.
A secondary locking means is shown comprising a length of load
limiting wire 5 having its end portions extending into two holes 10
in the spool body 1 and passing through a locking element 4 and
through a locking wheel 6 forming part of the locking assembly
2.
FIG. 2 is a perspective view of a locking wheel assembly for one
end of the seat belt retractor of FIG. 1. The orientation of the
wire is shown more clearly in FIG. 2 wherein the wire 5 extends
axially through and beyond the locking wheel 6 to be received in
the holes 10 in the spool. As used herein and in the claims the
terms "axial" and "axially" are understood to refer to orientations
of components either along or substantially parallel to the axis of
rotation of the spool when the spool is mounted in a retractor
frame.
The wire 5 holds the locking element 4 out of engagement with the
locking wheel 6 against the action of a spring load.
If a crash a sensor attached to the seat belt retractor detects a
sudden change in speed or direction of the vehicle a lock bar (not
shown) is moved to engage teeth 12 on the locking wheel 6 to lock
the spool 1 against rotation, subject to movement due to load
limiting arrangements. A lock bar can be seen in the prior art
retractor shown FIG. 10 and is identified by reference character
110. Once the spool 1 is locked the crash force transfers to the
torsion bar 3 and above a predetermined value causes the torsion
bar to twist about its axis allowing the spool 1 to rotate under
conditions determined by the properties of the torsion bar 3.
Usually the spool 1 rotates up to two additional turns.
During this time the wire 5 is also being pulled out of the holes
10 in the body of the spool 1 providing an additional secondary
load limiting effect during a first stage of operation. The
combination of the torsion bar 3 and the secondary load limiting
wire 5 raises the initial load limiting threshold giving a higher
combined level of load limiting than the torsion bar alone, i.e.
holding the vehicle occupant back in his seat until an airbag is
fully deployed to share the restraining load.
At the end of the first stage (identified in the graph in FIG. 9),
at the point where the airbag is fully deployed, the wire 5 has
been fully pulled out of the holes 10 in the spool body 1 releasing
the locking element 4 to eject into the locking wheel 6 and engage
into a recess 7 in the locking wheel 6. Thus during a second stage
(identified in the graph in FIG. 9) the locking wheel 6 continues
to turn under the influence of the crash forces until the locking
element 4 reaches an abutment 8 at the end of the recess 7. At this
point the locking element 4 connects the spool 1 and the locking
wheel 6 together preventing any further load limiting and this
constitutes a third stage of operation (identified in the graph in
FIG. 9). The length of the recess 7 and the position of the
abutment 8 can be varied to modify the crash curve as required by a
vehicle manufacturer's specification, by providing a longer or
shorter dwell period at the torsion bar only load level (second
stage). Ideally the abutment 8 isn't reached in a first impact.
In the third stage of operation (identified in the graph in FIG. 9)
the seat belt retractor functions as a standard retractor without
any load limiting function and will restrain the vehicle occupant
appropriately for a second impact. This is particularly important
because the airbag will usually have deployed in a first impact and
thus the seat belt is the only restraint acting on the vehicle
occupant.
FIGS. 3 and 4 show the end of the first stage of operations
(identified in the graph in FIG. 9) wherein the wire 5 has been
fully pulled out of the holes 10 in the body of the spool 1 and
bent around into a space in the locking wheel 6. At this point the
locking element 4 is released from the body of the spool 1 and its
spring load ejects it into the recess 7 in the locking wheel 6 to
connect the spool to the locking wheel 6 and start the second stage
of load limiting. The spool 1 continues to turn under the influence
of crash forces as the torsion bar continues to twist and the
locking element 4 moves relative to the locking wheel 6 as shown in
FIG. 6 by sliding along the recess 7 until it reaches the stop
abutment 8.
When the locking element 4 contacts the abutment 8 as shown in
FIGS. 7 and 8 the locking element 4 is locked with the locking
wheel 6 and no further load limiting is effective. This third stage
(identified in the graph in FIG. 9) puts the retractor into a
standard operational format whereby the spool 1 is locked against
webbing payout and thus restrains the vehicle occupant effectively
against secondary crash forces.
FIG. 9 is a digressive load limiting graph showing how a vehicle
occupant feels a crash force over a period of time. At T.sub.0 a
crash occurs causing a sudden deceleration or change of direction
of the vehicle which is detected by a crash sensor and brings the
locking mechanism into effect. During the period T.sub.0 to T.sub.1
the crash forces on the vehicle occupant increase linearly to a
force level F.sub.1. At T.sub.1 the first stage of operation comes
into effect provided by the wire 5 and the torsion bar 3 acting
together to provide load limiting and the force levels out at
F.sub.1 during the period T.sub.1 to T.sub.2. At time T.sub.2 the
wire 5 is fully extended and the locking element 4 is released to
move relative to the locking wheel 6. Thus the force felt by the
vehicle occupant decreases to a level F.sub.2 provided by the
torsion bar 3 alone. During the second stage over the period
T.sub.3 to T.sub.4 only the torsion bar provides load limiting
while the locking element 4 moves around the recess 7. At time
T.sub.4 the locking element 4 engages the abutment 8 and locks the
seat belt retractor fully, preventing further twisting of the
torsion bar 3. From time T.sub.4 onwards the seat belt retractor is
fully locked and acting as a standard seat belt retractor with no
load limiting. The vehicle occupant will feel linearly increasing
forces during this third stage. However, by this time the crash
forces from the primary impact will usually have dissipated. The
graph shows the situation for a secondary impact at around time
T.sub.4.
Although this invention has been described by way of example and
with reference to possible embodiments thereof, it is to be
understood that modifications and improvements may be made without
departing from the spirit or scope of the invention.
* * * * *